Resilient split core and shell for moulding apparatus



Dec. 1, 1964 s. s. PAvlcEvlc 3,158,907

REISILIENT SPLIT CORE AND SHELL FOR MOULDING APPARATUS Filed Nov. 14, 1962 2 Sheeizs-Sheel 1 Dec. 1, 1964 S. s. PAvlcEvlc 3,158,907

RESILIENT SPLIT CORE AND SHELL FOR MOULDING APPARATUS Filed Nov. 14, 1962 2 Sheets-SheetI 2 United States Patent O 3,l58,9l7 PLlT CGR?, AND SHELL FR MQTULEDIG APFARAUS Strahinga S. Paviceuie, Putzhrunnerstrasse ll, lttohrunn, naar Munich, Germany Filed Nov. 14, E662, Ser. No. 237,59l Claims prieriy, application Austria, Nov. i4, $51, A 8,5'7e/6l 4 (Cl. l8-45) This invention relates to moulds for the production of fabric-reinforced plastic pipes and tubes, the mould comprising an outer shell, an cxpansible core, and means for forming a fluid-tight seal between the shell and the core at each end.

ln a known mould of this kind, the core consists of a rigid cylindrical tube enclosed in an expansible tubular rubber sheath, means being provided for introducing a pressurised fluid, such as compressed air, between the inner tube and the expansible sheath. It is a drawback of such a mould that a fabric-reinforced plastic tube cannot be produced with constant Wall thickness throughout, because regions of the tube which initially didier in thickness owing to differences in the thickness of the fabric reinforcement are all exposed to the same radial pressure.

For the production of seamless sleeves from fabrics impregnated with a synthetic resin it has been proposed to use a mould with a longitudinally divided core adapted to be mechanically expanded by the introduction of a tapering mandrel. However, this kind of mould is unsuitable for producing longer sections of tube, for instance several metres in length.

For the continuous mass production of the outer covers of vehicle tires an expanding mould is also known which permits the divided and overlapping core of the mould to be expanded mechanically.

lt is an object of the present invention to provide a simple and effective mould for the production of dimensionally accurate and satisfactory glass-iibre-reinforced plastic tubing in relatvely long lengths and of relatively large diameter in such manner that the plastic tubes thus produced will satisfy the strictest requirements.

Accordingly to the present invention the shell of the mould which, in conventional manner, shapes the outside of the reinforced plastic tube is a robust, preferably metallic, tube and the core of the mould which shapes the inside of the plastic tube is a single longitudinally split tube of resilient material with overlapping longitudinal edges, the outer of Whch tapers in thickness substantially to zero, a flexible heat resistant seal being interposed between the overlapped portions of the core.

Preferably, the length of the core corresponds exactly with the length of the shell, and the overlap of the edges in the free or unexpanded state of the core conveniently embraces at least one third of its circumference.

Advantageously the ends of the core are encased in detachable U-section seals of a resiliently expansible heatresistance substance.

Conventional end plates are detachably axed to the ends of the mould and the inside surfaces of these plates are preferably highly polished or chromium-plated. Annular compressible seals are preferably inserted between the end plates and the end edges of the shell, these seals being heat resistant and having an inside diameter at least equal to the internal diameter of the shell. They may be aiiixed to the edges of the shell or to the inside faces of the end plates.

At least one of the end plates is provided with a port for connecting the interior of the core with a source of pressure for expanding it; alternatively, the mould cavity ,l58,9@7 Patented Dee. 1, 1964 formed by the annular gap or clearance space between the core and the shell can be evacuated through another port by a suction pump for the same purpose.

The shell may be of multipart, preferably two-part construction and it may be provided with chambers for cooling or heating the interior of the mold.

Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

FlG. l is an axial section of an assembled mould before the core is expanded;

FlG. 2 is a view similar to FIG. 1 showing the core expanded during the moulding process;

FG. 3 is a fragmentary perspective view of the core;

FIG. 4 is a section on the line lV-IV of FIG. 3;

FlG. 5 is a cross-section of a moditied shell;

FIG. 6 is an axial section through one end of a mould for forming plastic pipes or tubes with socket ends, and

FIG. 7 is a view similar to FIG. 6 of a mould for producing reduced ended pipes.

eferring first to FIGS. 1 and 2, a mould according to the invention for producing -tubes or pipes of glassiibre-reinforced plastic comprises a relatively thick Walled metal tube ll forming an outer shell and capable of withstanding internal gauge pressures up to about 20 atmospheres. The internal surface of the shell is highly polished or chromium-plated to give a high iinish to the hardened plastic tube and facilitate its parting from the shell.

The core 2 of the mould, shown in greater detail in FIG. 3, is formed by a longitudinally divided resilient tube with peripherally overlapping longitudinal edges 3, 4, which tends to contract radially and is preferably made of spring steel. The overlap of the longitudinal edges 3 and 4 embraces at least one third of the periphery of the tubular core when at rest, and the other part is gradually tapered in thickness to substantially zero to present a fine edge.

Between the overlapped portions adjacent the edges 3 and d is placed a seal 6 (FlGS. 3 and 4). This seal may be fixed to the inside of the outer overlap portion, and 1nas a smooth low-friction surface. The external surface of the core 2, including the lapped portions, is highly polished or chromium plated to give a high internal iinish to the moulded plastic tube and enable it to be easily detached from the core.

The diameter of the core 2 is variable. In its normally contracted state its overall diameter is less than the internal diameter of the outer shell 1 by at least the maximum required wall thickness of the inished tube, and should be capable of being expanded in the free state to an outer diameter exceeding the internal diameter of the shell l by as much as 20% Without separation of the edges 3, d. The length of the core 2 is equal to that of the shell l so that when inserted into the shell the ends of the core and the shell are completely l'lush.

End plates 7, S are secured to each end of the outer shell l by clamps 9 which are only schematically indicated in FiGS. l and 2. One or both end plates 7, 8 are provided With a central inlet port l@ for connection with a source of compressed air for expanding the core 2. An air exhaust port il registers With the mould cavity formed by the annular gap or space between the core 2 and the shell l for connection to a vacuum pump so that air can be evacuated from this space. ln order to ensure va tight joint between the end plates '7, 8 and the core 2, the ends of the latter are litt-ed with detachable resilient U- section gaskets i3 which have smooth low-friction outer surfaces. Also between the end plates 7, 8 and the ends of the shell l are inserted resilient heat-resistant annular gaskets l2 which have nn inner diameter at least as large rial` and on its normal thickness.

iixed to the ends of the shell 1 or to the inside faces of the f end plates 7, 8. t

A glass-iibre-reinforcedV plastic tube is produced in a mould as described above in the following manner. The inside surface of the outer shell 1 and the outside surface ofthe split core tube 2, including the overlapped portions, are tirs/t coated with a conventional parting agent. The glass-nbre fabric L, Vimpregnatedvvith the liquid synthetic resin, is wound on to the core 2in one or several layers. The coreand its wrapping are, then inserted into the shell and the core is adjusted so that its ends are tiush with the ends of the'shell.Y The end plates 7,'8 are then clamped in position. A vacuum pump is then connected to the exhaus't port 11 to evacuate the clearance space or mould cavity between the shell and the core, and at the same time a compressor is connected to the inlet port 1t? and forces air into the core 2 until the core 2 expands, simultaneously stretching the resilient U-ring gaskets 13 at each end, so that the plastic-impregnated glass-fibre L is pressed Vagainst the inside of the shell 1 of the mould. The quantity of resin used for impregnating the glass-nbre fabric Vmust be selected to ensure that there is no surplus resin when the Vcore 2 has been fully expanded. The laminate Lis then hardened in conventional manner. Flhis process is determined by the nature of the synthetic'resin employed. t When the laminate L has hardened, the compressed air is released from the tubular core 2 and the end plates 7, 8 are detached. The core 2 contracts to its original size and the nished tube can be easily removed from the mould. In' the modification shown in FIG. 5, the shell 1 of the mould is double-walled and of two-part construction, forming semi-annular chambers 14, 15 into which superheated steam can be Vintroduced for setting the plastic. When the plastic tube has hardened, a coolant may be passed through these chambers. Y Y

In order to permit the ends of the finished tubes L to be ,inter-fitted, they mayV be formed with a socket end (FIG. 6) for insertion thereinto of the plainv spigot end of anotherV pipe or tube. For production oftubes of this kind one end of the shell 1 of the mould must be widened ou the inside at 1a and the core tube Z ared accordingly at thefsame end 2a. Alternatively, as illustrated in FIG. 7, one end of each plastic tube L may be necked. For making such tubes one end 1b of the shell 1 mustbe suitably reduced in diameter, for instance by the insertion of a short sleeve or bush 5 which is preferably fixed to the internalwall of the shell 1. The corresponding end 2b according to the present invention must be capable of *radial expansion over a Ygivenworking range of diameters without` risk oli-reduction of theV angular extent of overlapfof the longitudinal edgesy 3, 4 beyond a safe minimum. This minimum will be determined in any particular case partly by the need to` maintain an accurately cylindrical effectively continuousexternal wall surface Vduring expansion, and'partly by the need to maintain aneftective fluidpressure seal at all working pressures and diameterst The degree ot'Y taper of the outer overlapping portion or Vlayer will also depend on the resilience of the core mate- Clearly, a thinner or finer-'edge 3 can be permitted Vas the resilience is increased. t. Any convenient pressure fluid may be used to expand the coreV-ZV--for example, Voil or water may be pumpedV Y into the core through the inlet port 10 in place ofair or other gas. Where a liquid is used, its temperature maybe c'ontrolledsoV as to facilitate the most efficient hardening of the plastic tube being formed. To ensure the necespressure to cause expansion of the core may be continu- Y ouslyv circulated under the krequired pressure--as by convertingone ofthe inletV ports 10 into an outlet port.

Y' The permanently overlapped inner portion of the split V d tube adjacent the internal longitudinal edge 4 may be deformed from a cylindrical'contour in orderY to accommodate the pressure uid seal material 6. This seal must be capableV of withstanding the maximum working uid pressure diiierence required to be establishedy across the y t core in order to produce both the necessary radial expansion of the split tube and the exertion ofY the necessary radial pressure on the reinforced plastic tube during hardening thereof. It must also withstand the working temperature range of the-core 2 whilst imposing a minimum of frictional drag on the overlapping layers or zones of the tube wall.

I claim:

1. VA mould for producing reinforced plastic tubes and they like comprising a shell and a core within Ythetshell, and means for closing the ends of both the shell and the core in duid-tight manner, wherein thefcore is'formed by a single longitudinally split resilient expansible tube whose longitudinal edges overlap to an extent suflicient to allow the tube to expand at least to its normal working limit of diameter Without reduction ofthe extent of overlap below a sate minimum at which the tube continues to present an effectively continuous cylindrical outer surface under l Working conditions, means for introducing a fluid under pressure into the interior of the core tube, and a low friction duid pressure seal inserted between the overlapping portions of the resilient core tube.

2. A mould for producing reinforced plastic tubes and the like comprising a shell and a core, said shell comprising a cylindrical body, tianges formed on the ends of the shell, end plates covering the ends of the shell, a'resilient heat resistant annular gasket between each endV plate and the adjacent iange on the shell, means securing the end plates to the iianges of the shell, said corelying within the shell and comprising a longitudinally rdivided resilienttube with peripherally overlapping longitudinal edges which tend to'contract radially, thefouter edge portion tapering toward the end of the portion, a sealing material between the overlapped portions Vof the core, U-ring resilient gaskets embracing the ends of the core, said gaskets expanding in diameter when the core is expanded radially,

ing a cylindrical body with a smooth interior Vface therein, flanges formed on the ends of the shell, end plates covering the ends of the shell, a resilient heat resistant annular gasket between each end plate and the adjacent iiange on the shell, saidgasket having an internal diameter at least as large as the internal diameter of the shell, means securing the end plates, to the anges of the shell, said core lying Within the shell and comprising a longitudinally divided resilient tube with peripherally overlapping longitudinal edges which tend to contract radially and made of spring steel, the outer edge portion tapering Vtoward the end of the portion, a sealing material between the overlapped portions of the core, said material having a Y smooth low-friction surface, U-ring resilient gaskets embracing the ends of the core and slidingly engaging the interior faces of the end plates, said gaskets expanding in diameter when the-,core is expandedradially, and means in the end platesto provide for the admission of liuid under pressure to within the core and for the venting of air from the cylindrical space between the core and the shell.

4,. A mould for producing reinforced plastic tubesy and Y the like comprising a shell and a core within theY shell, and means for closing the ends of both the shell and the core in huid-tight manner, wherein the core includes longitudinally split` resilient expansible tubemeans WhoseV longitudinal edges overlap to an extent sufficient to allowV the tube means to expand' at least to a normal Working.

limit of diameter of the tube means Without reduction of extent of overlap below a safe minimum at which the tube means continues to present an effectively continuous cylindrical outer surface under Working conditions, means for introducing a uid under pressure into the interior of the core tube means, and a low-friction iluid pressure sealing means inserted between said overlapped portions of the resilient core tube means.

UNlTED STATES PATENTS References Ce by the Examiner 710,596 10/02 Morris 25-128 fc3 Georgenson. Maag.

Lake 25--128 Soule 25-128 Billner 25-128 Warnken 18-34 MICHAEL V. BRNDSI, Primary Examiner.

10 WILLIAM J. STEPHENSON, Examiner. 

1. A MOULD FOR PRODUCING REINFORCED PLASTIC TUBES AND THE LIKE COMPRISING A SHELL AND A CORE WITHIN THE SHELL, AND MENS FOR CLOSING THE ENDS OF BOTH THE SHELL AND THE CORE IN FLUID-TIGHT MANNER, WHEREIN THE CORE IS FORMED BY A SINGLE LONGITUDINALLY SPLIT RESILIENT EXPANSIBLE TUBE WHOSE LONGITUDINAL EDGES OVERLAP TO AN EXTENT SUFFICIENT TO ALLOW THE TUBE TO EXPAND AT LEAST TO ITS NORMAL WORKING LIMIT OF DIAMETER WITHOUT REDUCTION OF THE EXTENT OF OVERLAP BELOW A SAFE MINIMUM AT WHICH THE TUBE CONTINUES TO PRESENT AN EFFECTIVELY CONTINUOUS CYLINDIRCAL OUTER SURFACE UNDER WORKING CONDITION, MEANS FOR INTRODUCING A FLUID UNDER PRESSURE INTO THE INTERIOR OF THE CORE TUBE, AND A LOW FRICTION FLUID PRESSURE SEAL INSERTED BETWEEN THE OVERLAPPING PORTIONS OF THE RESILIENT CORE TUBE. 